docs: def transition(self, inputSymbol):
          """
          Transition between states, returning any outputs.
          """
          outState, outputSymbols = self._automaton.outputForInput(self._state,
                                                                   inputSymbol)
          outTracer = None
          if self._tracer:
              outTracer = self._tracer(self._state._name(),
                                       inputSymbol._name(),
                                       outState._name())
          self._state = outState
          return (outputSymbols, outTracer)